The invention relates to an improved industrial apparatus for the large-scale storage of energy and a process for storing and transporting electric energy by means of this apparatus.
The generation of electric energy is, in the case of fossil fuel-fired power stations, associated with the production of CO2 and therefore has a considerable influence on the greenhouse effect. Generation of energy on the basis of renewable energy carriers, e.g. wind, solar, geothermal or hydroelectric, avoids this disadvantage. However, these renewable energy carriers are at present not available whenever wanted in accordance with the consumption profile. In addition, the site of energy generation may be different from the site of energy consumption. To compensate this disadvantage inherent in the system, storage, buffering and possibly also transport of the energy generated is necessary.
The energy from renewable sources such as wind turbines, solar plants is not obtained continuously. Demand and availability are not matched. A power grid which is based exclusively on renewable energies and is nevertheless stable cannot be obtained under these boundary conditions. There is therefore a need to equalize and buffer these fluctuations by means of inexpensive and energy-efficient systems having a high efficiency.
In many sparsely populated regions of the earth, e.g. the Sahara, Iceland or “off-shore”, there is the potential of generating electric power quite efficiently from wind, sun or geothermal heat via wind power stations, solar plants or geothermal power stations because of the geographic, climatic and/or geological boundary conditions. However, there is a lack of industrial methods of transporting this energy to regions having a high consumption. Traditional transmission systems are limited by grid losses and costs of grid construction. Hydrogen technology in which electric energy produced is converted on site into hydrogen and subsequently converted into electric power in a fuel cell has an efficiency of about 20% and is therefore unattractive since transport and liquefaction of the hydrogen consume a major part of the energy.
Both the storage of large quantities of electric energy and the transport of electric energy over large distances is a problem which has not been solved satisfactorily to the present time. At present, pumped storage power stations in which the potential energy of the geodetic height difference of water is utilized for transformation into power are used for storing electric energies on an industrial scale. However, the construction of such pump storage power stations is limited by geographic and ecological boundary conditions. Pump storage power stations in which the compression of air is used for energy storage are limited because of their comparatively low efficiency. Other forms of energy storage, e.g. supercapacitors or the flywheel address other target markets (short-term storages). Batteries come closest to this requirement and have been realized industrially in various designs.
DE-A-2635900 discloses a battery which comprises at least one molten alkali metal as anode and a cathodic reactant whose reactivity with the anodic reactant is electrochemically reversible. The cathodic reactant comprises molten polysulfide salts or a two-phase composition composed of molten sulfur and polysulfide salts saturated with molten sulfur. This battery further comprises cation-permeable barrier layers for mass transfer between the anodic reaction zone and the cathodic reaction zone.
DE-A-2610222 discloses a battery comprising a plurality of sulfur-sodium cells, where each cell has 1) a cathodic compartment comprising a cathodic reactant 2) which is liquid at operating temperature and is composed of sulfur, phosphorus or selenium or alkaline salts of these elements, at least one solid electrolyte tube which comprises the anodic reactant which is liquid at the operating temperature and is composed of an alkali metal, in particular sodium, and also an anodic container 3) which comprises a reserve of the anodic reactant.
Connecting a plurality of sodium-sulfur batteries as module for an energy storage system is known from EP-A-116690.
All these batteries are closed systems whose energy storage is limited by the amount of reactants (redox partners) comprised in the battery. This limitation has been alleviated by the flow battery. This battery concept is based on liquid electrolytes comprising solvent and metal salt. The limited stock volume of the classical battery is increased by second stock vessels comprising the reactants.
DE-A-2927868 discloses a flow battery for storing and releasing electric energy in an electrochemical cell having an anode compartment and a cathode compartment which are separated from one another by a semipermeable ion-exchange membrane, where the anode compartment is supplied with an anolyte solution, an oxidizable compound which remains essentially dissolved in the anolyte solution and can be reduced again from its oxidized form, the oxidized anolyte solution is removed from the anolyte component and the oxidized anolyte solution is stored. At the same time, the catholyte compartment is supplied with a catholyte solution, a reducible compound which remains essentially dissolved in the catholyte solvent and can be reoxidized from its reduced form. The anolyte solution and the catholyte solution can be stored in two corresponding vessels and circulated through the anode compartment and cathode compartment by means of circulation pumps. The catholyte solution can, for example, comprise hexavalent chromium and the anolyte solution can comprise divalent chromium.
DE-A-1771148 and U.S. Pat. No. 3,533,848 disclose a system for obtaining electric energy by electrochemical combination of sodium and sulfur, wherein the system has a diaphragm permeable to sodium ions with adjacent spaces for sodium and sulfur, a container for storing the sodium outside the cell, lines for conveying the sodium from the storage container to the fuel cell, a container for storing the sulfur outside the cells and lines for conveying the sulfur from the storage container to the cell. These cells can, for example, be electrically connected in series.
It is known from JP-A-2001118598 that sodium-sulfur batteries can be operated with two or more cylinders in matrix form for molten sodium or molten sulfur.
It is known from JP-A-2002184456 that a sodium-sulfur battery can be operated with an external storage tank for sulfur which is connected in a fixed manner to the battery.
In the known sodium-sulfur batteries and their embodiments as flow battery, the input of the energy stored in the starting materials sodium and sulfur and the discharge by reaction of sodium and sulfur to form sodium sulfide and/or sodium polysulfides are coupled in time and space.